Is deduction of use in application to our everyday problems? Aristotle said that in practical matters we cannot use a strictly deductive attitude: "we must be content...in speaking about things which are only for the most part true, with premises of the same kind, to reach conclusions that are no better" (Nic.Eth.I,4 - my underlining). We may content ourselves with conclusions which - according to the usual views - are not true; but what happens when we realize that such conclusions bring us into contradiction with some of our deepest beliefs? We have to pursue our search of rationality in the most compelling manner, and this effort forces us to express our background beliefs in order to check what may be wrong with that. In this paper I will give two classical examples, one form the history of cinema and another from the history of artificial intelligence: in comparing these two examples I claim that logical compulsion - the deep need for convention - is highly valuable where feelings are not enough